Crack closure and rehabilitation of chloride contaminated reinforced concrete structures

ABSTRACT

Apparatus to electrodeposit a chemical composition into cracks in concrete filling same is disclosed. The apparatus is comprised of a dam (reservoir) which is placed over the crack to be filled, an electrolyte which is received within the dam (reservoir), a direct current power source and an electrode which is received within the electrolyte and acts as an anode. The steel reinforcing rods within the concrete act as the cathode. Application of direct current from the power source to the electrode and the reinforcing rods causes the electrodeposition of a chemical composition into the crack filling same and the repassivation of the reinforcing rods within the concrete.

TECHNICAL FIELD

The present invention relates, in general, to repairing cracks in chloride contaminated reinforced concrete structures and, more particularly, to the application of technology to electrodeposit a chemical composition into a crack to fill the crack and to repassivate the steel reinforcing rods in the concrete structure.

BACKGROUND ART

Steel reinforcing rods contained within concrete are protected against corrosion by the alkalinity of the cement within the concrete. The cement contains alkali, alkali earth, metal oxides and hydroxides that typically result in concrete having a pH of between 12 and 14 depending upon the source of the cement and its age. In a highly alkaline environment, the steel reinforcing rods are passivated by the formation of a surface oxide film that protects the steel from corrosion. This protective oxide film is relatively stable at pH values greater than approximately 12.5 in a chloride free environment. The pH value required to stabilize the protective oxide film increases as the chloride content within the concrete increases. If this protective film is broken, corrosion can commence on the steel reinforcing rods. This may occur as a result of the ingress of sufficient chlorides into the concrete matrix to initiate corrosion. The chlorides may originate from the use of deicing salts, exposure to a marine environment, or through the use of a concrete admixture that contains chlorides. Alternatively, or in combination with the ingress of sufficient chlorides, carbonation of the concrete can occur. Carbonation, which is the reaction of CO and CO₂ in the air with available alkali in the concrete, causes the pH of the concrete to decrease over time. Once the pH of the concrete is below 9.5, the protective oxide film starts to break down resulting in the commencement of corrosion of the steel reinforcing rods and the deterioration of the concrete structure. The deterioration of such structures has become a concern in the concrete industry. This concern has become so important that the issue of concrete durability has replaced the issue of concrete strength as the most pressing problem facing the concrete industry.

The objective of any type of concrete repair is for the repair to be relatively low in cost and durable in nature. In addition, variations in the repair should be limited and predictable over time and the repair should not deteriorate over time. Typically, there are several approaches to rehabilitate chloride contaminated reinforced concrete. One approach is to remove the damaged concrete and replace it with patch materials. Another approach is to utilize electrochemical means to minimize or eliminate future corrosion of the steel reinforcing rods within the concrete. Electrochemical chloride extraction typically involves the application of relatively high direct electrical currents to the concrete over a period of 10 to 50 days. The objective of this approach is to remove 20-50% of the chlorides from the concrete.

Another approach which is referred to as cathodic protection involves the passage of a small direct electrical current through the concrete. The objective of this approach is to reduce the rate of reinforcing rod corrosion to very low levels that are not of engineering significance. To apply an electrical current to the concrete, an anode is attached to the concrete and a voltage is applied between the anode and the steel reinforcing rods causing a direct current to flow through the concrete. With the cathodic protection approach, it is generally assumed that the protective current must be continually provided to the steel reinforcing rods.

Even though electrochemical approaches have been utilized to minimize or eliminate future corrosion of the steel reinforcing rods in concrete, such an approach does not fill the cracks within same. To fill such cracks, the injection of epoxy into same or routing and sealing the cracks or placing grout into the cracks are several of the approaches that have been utilized. Alternatively, electrodeposition of material into the cracks has been suggested. Such an approach, however, requires the crack to be immersed completely in an electrolyte solution. In many instances, immersion of the crack into an electrolyte solution is not possible.

In view of the foregoing, it has become desirable to develop an apparatus to electrodeposit a chemical composition into a crack in a chloride contaminated reinforced concrete structure in order to fill same while repassivating the steel reinforcing rods within the structure, even though the crack is not totally immersed in an electrolyte solution.

SUMMARY OF THE INVENTION

The present invention solves the problems associated with the prior art approaches to repair cracks in chloride contaminated reinforced concrete structures and other problems by applying technology to electrodeposit a chemical composition into the crack filling same. Such electdeposition requires the use of a dam (reservoir) which is placed over the crack to be filled, an electrolyte received with the dam (reservoir), a direct current power source and a steel mesh electrode which is received within the electrolyte and acts as an anode. The steel reinforcing rods within the concrete structure act as the cathode. The electrolyte is comprised of a composition of dialkylamino alkanoate zinc salt in isopropanol and natural spirits, and barium methaborate. Application of direct current by the power source to the steel mesh electrode and the steel reinforcing rods within the concrete structure causes the electrodeposition of a chemical composition into the crack in the concrete structure filling the crack and the repassivation of the steel reinforcing rods within the concrete structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view, partially broken away in cross-section, showing the present invention being used in conjunction with a concrete structure having a crack therein.

FIG. 2 is a top plan view of the concrete structure illustrating the crack in the surface thereof.

FIG. 3 is a graph of the rate of crack closure (percent width of the crack that is closed) versus the electrodeposition time (in hours) for various crack widths.

FIG. 4 is a graph of the rate of crack closure (percent length of the crack that is closed) versus the electrodeposition time (in hours) for various crack lengths.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the Figures where the illustrations are for the purpose of describing the preferred embodiment of the present invention and not intended to limit the invention described herein, FIG. 1 is a perspective view, partially broken away in cross-section, showing the apparatus 10 of the present invention being used in conjunction with a concrete structure 12 having steel reinforcing rods 14 therein. The surface 16 of the concrete structure 12 has a crack 18 formed therein. The apparatus 10 is comprised of a dam (reservoir) 20 which is placed over the crack 18 in the surface 16 of the concrete structure 12. An electrolyte 22, comprised of a composition of dialkylamino alkanoate zinc salt (about 2.5% by weight) in isopropanol and natural spirits, and barium methaborate (about 2.0% by weight), is received within the dam (reservoir) 20. A steel mesh electrode 24 is received within the electrolyte 22. A direct current source 26 acts as a power supply and has its positive terminal connected to the steel mesh electrode 24 and its negative terminal connected to the steel reinforcing rods 14 within the concrete structure 12. The application of direct current by the current source 26 to the electrode 24 and the steel reinforcing rods 14 over a period of time causes the crack 18 in the surface 16 of the concrete structure 12 to be filled by the electrodeposition of a chemical compound therein providing a physical barrier to the further intrusion of corrosive material into the concrete structure 12. While the foregoing electrodeposition process is occurring, the steel reinforcing rods 14 are repassivated preventing the further corrosion thereof.

Referring now to FIG. 2, a top plan view of the concrete structure 12 with the crack 18 in the surface 16 thereof is illustrated. The dam (reservoir) 20 is placed over a portion of the crack 18 in the surface 16 of the concrete structure 12. In this instance, the dam (reservoir) 20 is placed over a portion of the crack 18 such that it covers two crack areas, viz., area II and area I. As shown in the chart adjacent to FIG. 2, the portion of the crack 18 in area II that is covered by the dam (reservoir) 20 has a depth of 25 mm, a width of 2.5 mm and a length of 120 mm. In addition, the portion of the crack 18 in area I that is covered by dam (reservoir) 20 has a depth of 25 mm, a width of 2 mm and a length of 20 mm. Also, the portion of the crack 18 in area I that is not covered by dam (reservoir) 20 has a depth of 25 mm, a width of 2 mm and a length of 75 mm. In addition, the portion of the crack 18 in area III that is not covered by dam (reservoir) 20 has a depth of 20 mm, a width of 1.5 mm and a length of 85 mm.

Referring now to FIG. 3, which should be used in conjunction with FIG. 2, a graph of the rate of crack closure (percent width of the crack that is filled or closed) versus the electrodeposition time (in hours) for various crack widths, such as the crack width of 2 mm in area I, 2.5 mm in area II and 1.5 mm in area III, is illustrated. It can be seen from this graph that electrodeposition within the crack 18 commences after about seven hours of the application of direct current from the current source 26 to the electrode 24 and the steel reinforcing rods 14 and that significant electrodeposition has occurred after about thirteen hours of the application of the aforementioned direct current. In addition, it should be noted that 100 percent electrodeposition in area II of the crack 18 has occurred after about nineteen hours of the application of the aforementioned direct current. Furthermore, it should be noted that after about nineteen hours of the application of the aforementioned direct current, approximately 75% of the width of the portion of crack 18 in area I has been filled even though a significant portion of the crack in area I is not covered by dam (reservoir) 20 and that approximately 47% of the width of the portion of crack 18 in area III has been filled even though this portion of the crack 18 is not covered by the dam (reservoir) 20.

Referring now to FIG. 4, which should be used in conjunction with FIG. 2, a graph of the rate of crack closure (percent length of the crack that is filled or closed) versus the electrodeposition time (in hours) for cracks having various lengths, such as the crack lengths shown in area I, area II and area III, is illustrated. As in FIG. 3, electrodeposition within the crack 18 commences after about seven hours of the application of direct current from the current source 26 to the electrode 24 and the steel reinforcing rods 14. This electrodeposition is significant after about thirteen hours of the application of the aforementioned direct current and is substantial after about nineteen hours. As can be seen, after about nineteen hours of the application of the aforementioned direct current, approximately 100% of the portion of the crack 18 in area II has been filled and approximately 60% of the portion of the crack 18 in area I has been filled even though a significant portion of the crack in area I is not covered by the dam (reservoir) 20. Furthermore, after about nineteen hours of the application of the aforementioned direct current, approximately 40% of the portion of the crack 18 in area III has been filled even though this portion of the crack 18 is not covered by the dam (reservoir) 20.

From the foregoing, it is apparent that the present invention can be successfully applied to reinforced concrete structures that are not totally immersed in electrolyte permitting the filling of cracks that are located in any area of the structure. In addition to filling the cracks in the concrete structure, the present invention repassivates the steel reinforcing rods within the structure. Thus, the present invention restores the integrity of the reinforced concrete structure by filling the cracks therein and by repassivating the steel reinforcing rods within the structure, and coats the concrete surface with chemical compounds that provide a physical barrier to the further intrusion of corrosive material into the concrete.

Certain modifications and improvements will occur to those skilled in the art upon reading the foregoing. It is understood that all such modifications and improvements have been deleted herein for the sake of conciseness and readability, but are properly within the scope of the following claims. 

1) Apparatus for electrodepositing a chemical composition into a crack in concrete having reinforcing rods therein comprising a reservoir for placement over the crack in the concrete, an electrolyte received within said reservoir, an electrode received within said electrolyte and an electrical power source having a first terminal connected to said electrode and a second terminal connected to said reinforcing rods within the concrete. 2) The apparatus as defined in claim 1 wherein said electrolyte is comprised of a composition of dialkylamino alkanoate salt and barium methaborate. 3) The apparatus as defined in claim 2 wherein said dialkylamino alkanoate salt is in isopropanol and natural spirits. 4) The apparatus as defined in claim 2 wherein said dialkylamino alkanoate salt is about 2.5% by weight of said composition. 5) The apparatus as defined in claim 2 wherein said barium methaborate is about 2.0% by weight of said composition. 6) The apparatus as defined in claim 1 wherein said electrode is formed from steel mesh. 7) The apparatus as defined in claim 1 wherein said electrical power source is a direct current power source. 